On the basis of the two versions R8 and R9, the version R10 of the Long Term Evolution (LTE) system adds many new features, for example, pilot characteristics such as DMRS (Demodulation Reference Signal) and CSI-RS (Channel State Information Reference Signal), and transmission and feedback characteristics such as eight antenna supporting, especially the eICIC (enhanced Inter-Cell Interference Cancelling) technology, which further considers the inter-cell interference cancelling technology on the basis of considering the R8/9 ICIC.
Technologies for solving the problem of inter-cell interference mainly consider avoiding inter-cell interference in a homogeneous network at the early stage of the R10, wherein the mainstream considerations are the eICIC technology and the CoMP (Coordinated Multi-point) technology. The CoMP, as the name suggests, is multiple nodes coordinating to send data to one or more user equipments (UE) in the same or different time-frequency resources. Such technologies can reduce inter-cell interference, increase throughput at the cell edge, and expand the cell coverage. However, since discussions at the later stage take the heterogeneous network into consideration and introduce more scenarios, and also due to the complexity of CoMP technology and the limited time for R10 discussion, it was finally determined that no extra CoMP standardized content would be introduced at the R10 stage, but the needs of CoMP part can be considered when designing the CSI-RS, therefore there has been no further discussion on the CoMP technology after the 60bis conference.
The LTE defines that the PDCCH (Physical downlink control channel) bears scheduling and allocating and other control information, and each PDCCH is composed of a plurality of CCEs (Control Channel Elements), and the number of CCEs of each subframe is determined by the number of PDCCHs and the downlink bandwidth.
The UE obtains the PDCCH by performing a blind detection in the search space. The search space is divided into a common search space and a UE-specific search space; the common search space refers to a region which all UE can search, and this space carries the cell specific information; the specific search space is a space range which an individual UE can search, and the specific search spaces of a plurality of UEs are likely to overlap, but generally the initial search positions are not the same. Before the blind detection, a high layer signaling is used to notify the UE of working mode and the type of Radio Network Temporary Identity (RNTI) used for cyclic redundancy check (CRC) scrambling of the PDCCH.
The relationship between the search space Sk(L) and the aggregation level L as well as the number of candidate PDCCHs M(L) is shown in Table 1. The aggregation level is the number of CCEs occupied by the PDCCH. When a blind detection is performed in the UE-specific search space, the UE first calculates the initial position Yk of the blind detection according to the user identity (UE ID) and the subframe number, and then performs detection in the search space until the PDCCH assigned to itself is detected.
TABLE 2PDCCH candidate setSearch space k(L)The numberAggregationSizeof candidatelevel [the number PDCCHs TypeLof CCEs]M(L)UE-specific16621264828162Common41648162
The correspondence of the aggregation level and the relative positions of the first control channel element of PDCCH in the UE-specific search space is shown in Table 2.
The relative position of the first control channel element of PDCCH in the UE-specific search space refers to the relative position of the first CCE index nCCE occupied by the PDCCH to the initial position Yk of the blind detection, and it is indicated as nCCE, offset in this specification, nCCE, offset=nCCE−Yk, and the value range of nCCE, offset is 0˜6, 8, 10.
TABLE 2Correspondence of the aggregation level and the first CCE positionAggregation The relative position of the first CCE levelin the UE-specific search spaceL = 1nCCE, offset = 0/2/4/1/3/5L = 2nCCE, offset = 0/4/8/10L = 3nCCE, offset = 0/4L = 4nCCE, offset = 0/8
In the SI (Study Item) stage of the R11, the main consideration is in Scenario4, and since different nodes have the same cell ID, if at this time the TM8 or TM9 is used for data transmission, the conventional DMRS sequence initialization expression is:cinit=(└ns/2┘+1)·(2NIDcell+1)·216+nSCID  eq. (1)
As can be seen from this equation that, the DMRS sequence is only related to time slot index (ns), cell ID (NIDcell), and scrambling sequence indication identity nSCID, taking into account that respective nodes in the same cell are fully synchronized, and nSCID, can only take the value of 0 or 1, and when the UEs of different nodes use the same sequence to send the DMRS, it will lead to strong DMRS interference between different nodes, which would limit the cell splitting gain under the Scenario4. Therefore, it considers introducing new parameters to make different nodes have different DMRS, which randomizes DMRS interferences between different nodes, thereby further obtaining the cell splitting gain under the Scenario4.
Then considering the Scenario3, since different nodes have different Cell IDs, if there is a UE located at the edge of two nodes, considering that the UE can perform multi-user multiple input multiple output (MU-MIMO) transmission with any UE in these two nodes, in order to ensure the orthogonality between two UEs, it needs to equip the edge UE with a NIDcell notification, especially when the edge UE is a UE which is currently performing the DPS (Dynamic Point Selection).
In the method for notifying the virtual ID, one consideration is to use a high layer signaling to notify the UE of the set of multiple virtual IDs, then nSCID is used to indicate that it is which virtual ID in the set of multiple virtual IDs, wherein each virtual ID may be referred to as a set of virtual signalings.
Furthermore, when considering that the UE transmits in two layers, because it needs to ensure the transparency of the MU-MIMO to the UE, the DMRS maximally supports the orthogonality of two DRMS ports, that is, in order to ensure a full orthogonality, it requires that the maximum number of layers of the UE of two MU-MIMO is two. Therefore, for a two-layer transmission, it can mainly focus on the effect of randomization, but for a one-layer transmission, it can mainly focus on the effect of orthogonality. Considering the effect of randomization, there are technologies proposing the following expression:cinit=(└ns/2┘+1)·(2X+1)·216+Y  Eq. (2)
Wherein X indicates the virtual ID, Y indicates the virtual scrambling indication information, X and Y can be indicated via a common dynamic or semi-static signaling. In this method, X and Y can be called as representing a set of virtual signalings.
Considering that in order to avoid the interference between demodulation pilots of different nodes in the heterogeneous network scenario, it can consider ensuring the DMRS orthogonality of different nodes, and the orthogonality of four users is maximally supported, then the flexible allocation of ports can be used to achieve this objective.